Lichen

Lichen are composite organisms arising from a symbiotic relationship between fungi (the mycobiont) and photosynthetic algae or cyanobacteria (the photobiont). This mutually beneficial relationship allows lichens to survive in diverse and often extreme environments where neither partner could survive alone.

Characteristics: Lichens exhibit a wide range of forms and colors, often appearing as crusts, foliose (leaf-like) structures, or fruticose (shrub-like) structures. They can be found growing on a variety of surfaces including rocks, trees, soil, and even animal shells. Lichens reproduce through several methods, including fragmentation, the dispersal of specialized structures called soredia and isidia, and sexual reproduction of the fungal partner. They obtain nutrients from the air, rainwater, and dust.

Symbiotic Relationship: The fungal partner provides the overall structure and protection, shielding the algae or cyanobacteria from excessive sunlight and desiccation. The fungus also efficiently absorbs water and nutrients from the environment. The photobiont, through photosynthesis, provides the fungus with carbohydrates and other organic compounds essential for energy.

Ecological Importance: Lichens are important components of many ecosystems. They contribute to soil formation by breaking down rocks, fix atmospheric nitrogen (particularly those with cyanobacteria as the photobiont), and provide food and shelter for invertebrates and other animals. They are also sensitive to air pollution and are thus used as bioindicators to assess environmental quality.

Human Uses: Lichens have been used by humans for a variety of purposes, including as a source of dyes, medicines, food, and as a traditional ingredient in perfumes.

Classification: Lichens are classified based on the fungal partner. Most lichens are ascomycetes (sac fungi), but some are basidiomycetes (club fungi).

Threats: Lichens are particularly vulnerable to air pollution and habitat loss. Their slow growth rate also makes them slow to recover from disturbances.